Exhaust gas heat exchanger

ABSTRACT

An exhaust gas heat exchanger has a tank, laminated exhaust gas tubes where the exhaust gas flows, a cooling water inlet pipe and a cooling water outlet pipe. The cooling water flows into the tank and flows through water passages between adjacent exhaust gas tubes and between an inner wall of the tank and an outermost exhaust gas tube. Ribs are formed on the exhaust gas tubes so as to lead the cooling water after colliding with an inner wall toward an upstream side of the exhaust gas tubes to prevent the cooling water from being stuck. Otherwise, spaces between an inner wall of a casing and the exhaust gas tubes are regulated to keep the flow rate of the cooling water in the casing so that the cooling water is prevented from being boiled locally by slow flow rate of the cooling water.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. Ser. No. 10/189,957filed on Jul. 53, 2002 based upon Japanese Patent Applications No.2001-209335, filed on Jul. 10, 2001, No. 2002-7333, filed on Jan. 16,2002, and No. 2002-494, filed on Jan. 7, 2002, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust gas heat exchanger forperforming heat exchange between exhaust gas generated by combustion andcooling water. Specifically, the present invention relates to an exhaustgas heat exchanger for cooling the exhaust gas in an exhaust gasrecirculation system (i.e., EGR system).

2. Related Art

As shown in FIGS. 1A and 1B, as a prototype made by the inventors, anexhaust gas heat exchanger for cooling the exhaust gas in an EGR system(hereinafter, referred to as an EGR gas heat exchanger 300) can beequipped with plural laminated exhaust gas tubes 301 disposed in a tank302 having a rectangular sectional pipe shape. The exhaust gas tubes 301have a flat sectional shape, and are attached to a core plate 303 whichcloses the tank 302. A cooling water inlet pipe 304 and a cooling wateroutlet pipe 305 are connected to the tank 302 so that cooling waterflows in the tank 302 to exchange heat with the exhaust gas passingthrough the exhaust gas tubes 301.

In this prototype, the inventors have found that the cooling water mightbe boiled at a location close to an upstream side of the exhaust gastubes 301. The boiling of the cooling water may cause less efficiencyabout cooling of the exhaust gas flowing through the exhaust gas tubes301, and/or rapid increase of inner pressure of the tank 302 that maydegrade durability of the tank 302.

The inventors performed an experiment to visually observe the stream ofthe cooling water flowing in an EGR gas heat exchanger that has fourexhaust gas tubes.

According to this experiment, when the cooling water inlet pipe isconnected to the tank 302 so as to be disposed substantiallyperpendicular to a longitudinal direction of the exhaust gas tubes 301,the cooling water flows into each passage formed between each adjacentexhaust gas tubes 301 so as to turn approximately perpendicular as shownby arrows A (cooling water stream A) in FIG. 2, and it flows toward thecooling water outlet pipe 305. Moreover, some of the cooling watercollides (impacts) with an inner wall 302 a of the tank 302 that isopposite to the cooling water inlet pipe 304 as shown by arrows B(cooling water stream B) in FIG. 2, and then, it flows toward an exhaustgas pipe 301 located at an outermost side.

However, the cooling water stream A coming from the cooling water inletpipe 304 and the cooling water stream B coming through the passagesformed between each adjacent exhaust gas tubes 301 interfere with eachother at the gaps formed between the inner walls 302 a and the outermostexhaust gas pipes 301. As a result, the cooling water is easily stuck inthe vicinity of the root portions of the exhaust gas pipes 301 where theexhaust gas pipes 301 are fixed to the core plate 303, as shown in FIGS.1 and 3.

This means it may be possible to boil the cooling water when the coolingwater is stuck in the vicinity of root portions of the exhaust gas pipes301 of an upstream side of the exhaust gas. As a result, the efficiencyfor exchanging heat may be lowered.

Moreover, the local boiling of water may be caused by low flowing rateof the cooling water in the tank 302.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an exhaust gas heatexchanger capable of eliminating the boiling of cooling water that maybe caused by the sticking of the cooling water or caused by low flowingrate of the cooling water.

The exhaust gas heat exchanger has a tank, a plurality of exhaust gaspassages provided in the tank through which exhaust gas flows and awater passage of the tank through which cooling water flows from acooling water inlet tube to a cooling water outlet pipe.

According to an aspect of the present invention, a guide is provided inthe tank to lead the cooling water that collides with an inner wall ofthe tank and flows so as to oppose the cooling water coming from thecooling water inlet pipe at an upstream side of the exhaust gaspassages.

With this guide, the cooling water that collides the inner wall of thetank is led to a portion where the cooling water can contact upstreamside portions of the exhaust gas passages. As a result, the coolingwater is prevented from being stuck in the vicinity of the upstream sideportions of the exhaust gas passages where the temperature of theexhaust gas is high, thereby preventing the cooling water from beingboiled.

Preferably, the guide is provided in an exhaust gas heat exchanger inwhich the cooling water inlet pipe is provided on the tank so that thecooling water flows into the tank through the cooling water inlet pipein a direction substantially perpendicular to a laminated direction ofthe exhaust gas passages and substantially perpendicular to alongitudinal direction of the exhaust gas passages, since the stickingof water easily occurs in this type of an exhaust gas heat exchanger.

Preferably, the guide is formed so as to protrude from an outer wall ofat least one of the exhaust gas passages.

With this feature, the guide is used as a reinforcing portion for thepassage for the cooling water.

According to another aspect of the present invention, a first bonnet forintroducing the exhaust gas to the plurality of exhaust gas tubes isprovided at one side of the tank, and a second bonnet for gathering theexhaust gas passing through the exhaust gas tubes. Moreover, a firstplate is provided between the first bonnet and a cooling water passagefor isolating the cooling water from the first bonnet, and a secondplate is provided between the second bonnet and the cooling waterpassage for isolating the cooling water from the second bonnet.Furthermore, a guide is provided in the tank to lead the water thatcollides at an inner wall of the tank and flows so as to oppose thewater coming from the cooling water inlet pipe to the vicinity of theroot portions of the plurality of exhaust gas tubes that are attached tothe first plate.

With this guide, the water that collides at an inner wall of the tank isled to the root portions of the plurality of exhaust gas tubes where theplurality of exhaust gas tubes are attached to the first plate. As aresult, the cooling water is prevented from sticking in the vicinity ofthe root portions of the plurality of exhaust gas tubes where theexhaust gas having high temperature flows into the plurality of exhaustgas tubes, thereby preventing the cooling water from being boiled.

According to further aspect of the present invention, a partition wallis provided between an outermost water passage for the cooling waterthat is formed between an inner wall of the tank and an outermostexhaust gas passage and an inner water passage for the cooling waterthat is formed between adjacent exhaust gas passages.

With this partition wall, after the cooling water collides with theinner wall of the tank, the cooling water is prevented from flowing intothe outermost passage formed between the inner wall and the outermostexhaust gas passage. Therefore, sticking of the cooling water at anupstream side of the plurality of exhaust gas passages, which is causedby the flow of the cooling water toward the outermost water passageformed between the inner wall and the outermost exhaust gas passage, isprevented, thereby preventing the cooling water from being boiled.

According to further another aspect of the present invention, an exhaustgas heat exchanger has a casing, a plurality of exhaust gas tubesprovided in the casing through which exhaust gas flows and each of whichhas flat sectional shape, and a fluid passage of the casing throughwhich fluid flows from a fluid inlet to a fluid outlet. In this exhaustgas heat exchanger, adjacent exhaust gas tubes are spaced apart fromeach other at a distance of δ t. Moreover, an outermost exhaust gas tubeof the plurality of exhaust gas tubes is spaced apart from an inner wallof the casing that faces the outermost exhaust gas tube at a distance ofδ in1 in a direction generally perpendicular to an inflow direction ofthe fluid coming into the casing through the fluid inlet and generallyperpendicular to a longitudinal direction of the plurality of exhaustgas tubes. The distance of δ in1 is substantially equal to the distanceof δt to prevent flow rate of the fluid from being lowered lower than apredetermined rate.

According to further another aspect of the present invention, an exhaustgas heat exchanger has a casing, a plurality of exhaust gas tubesprovided in the casing through which exhaust gas flows and each of whichhas flat sectional shape, and a fluid passage provided in the casingthrough which fluid flows from a fluid inlet to a fluid outlet. In thisexhaust gas heat exchanger, the fluid inlet is provided on the casing sothat the fluid can flow into the casing in a direction substantiallyperpendicular to a longitudinal direction of the plurality of exhaustgas tubes. Moreover, an outermost exhaust gas tube of the plurality ofexhaust gas tubes is arranged in the casing so as to be spaced apartfrom an inner wall of the casing at a distance of δ in1 in a directiongenerally perpendicular to an inflow direction of the fluid from thefluid inlet and in a direction generally perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes. Thedistance δ in1 is equal to or greater than 1 mm but less than or equalto 5 mm.

With this distance δ in1, a flow rate of the fluid flowing through aspace between the outermost exhaust gas tube and the inner wall of thecasing can be prevented from being lowered lower than a predeterminedflow rate.

According to further another aspect of the present invention, an exhaustgas heat exchanger has a casing, a plurality of exhaust gas tubesprovided in the casing through which exhaust gas flows and each of whichhas flat sectional shape, and a fluid passage of the casing throughwhich fluid flows from a fluid inlet to a fluid outlet. In this exhaustgas heat exchanger, the fluid outlet is provided on the casing so thatthe fluid flowing through the casing flows out from the casing in adirection generally perpendicular to a longitudinal direction of theplurality of exhaust gas tubes and in a direction generally parallelwith an arranged direction of the plurality of exhaust gas tubes. Anadjacent exhaust gas tubes are spaced apart from each other at adistance of δ t. Moreover, an outermost exhaust gas tube of theplurality of exhaust gas tubes is spaced apart from an inner wall of thecasing that faces the outermost exhaust gas tube at a distance of δ outin the vicinity of the fluid outlet with respect to the fluid inlet in adirection generally perpendicular to the longitudinal direction of theplurality of exhaust gas tubes and generally parallel with the arrangeddirection of the plurality of exhaust gas tubes. The distance δ out isgreater than the distance of δ t.

With this feature, pressure loss of the fluid in the casing is preventedfrom increasing, thereby preventing mass flow of the fluid fromdecreasing. Therefore, the effect of heat exchange between the fluid andthe exhaust gas is prevented from decreasing, and local boiling of thefluid is prevented.

Preferably, the distance δ out is greater than or equal to 5 mm.

Incidentally, the plurality of exhaust gas tubes may be spaced apartfrom an inner wall of the casing at a distance of δ in2 in a directiongenerally parallel with the inflow direction of the fluid coming intothe casing through the fluid inlet and generally perpendicular to alongitudinal direction of the plurality of exhaust gas tubes. Thedistance δ in2 is greater than or equal to the distance δ out. Thisdistance δin2 improves the distribution efficiency of the fluid to eachspace between the adjacent exhaust gas tubes and allows the pressureloss in the vicinity of the fluid inlet to be reduced.

Preferably, the distance δ in2 is greater than or equal to 1 mm tosecure the distribution efficiency of the fluid to each space betweenthe adjacent exhaust gas tubes and the reduction of the pressure loss.

Other features and advantages of the present invention will become moreapparent from the following detailed description made with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial cross sectional view showing an EGR gas heatexchanger in the related art;

FIG. 1B is a partial cross sectional view of the EGR gas heat exchangerin the related art taken along line IB-IB in FIG. 1A;

FIG. 2 is a partial cross sectional view similar to FIG. 1B of the EGRgas heat exchanger in the related art;

FIG. 3 is a partial cross sectional view of the EGR gas heat exchangertaken along line III-III in FIG. 1A;

FIG. 4 is a schematic view of an EGR system according to the presentinvention;

FIG. 5A is a partial cross sectional view of an EGR gas heat exchangerin a first embodiment of the present invention;

FIG. 5B is a partial cross sectional view of the EGR gas heat exchangerin the first embodiment of the present invention taken along line VB-VBin FIG. 5A;

FIG. 6A is a partial cross sectional view of an EGR gas heat exchangerin a second embodiment of the present invention;

FIG. 6B is a partial cross sectional view of the EGR gas heat exchangerin the first embodiment of the present invention taken along lineVIB-VIB in FIG. 6A;

FIG. 7 is a cross sectional view of the EGR gas heat exchanger in thefirst embodiment of the present invention taken along line VII-VII inFIG. 6B;

FIG. 8 is a perspective view of the EGR cooler in third and fourthembodiments of the present invention;

FIG. 9A is a partial cross sectional view of an EGR cooler in the thirdembodiment of the present invention;

FIG. 9B is a partial cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line IXB-IXB in FIG. 9A;

FIG. 10 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line X-X in FIG. 9B;

FIG. 11 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line XI-XI in FIG. 9B;

FIG. 12 is a cross sectional view of the EGR cooler in the thirdembodiment of the present invention taken along line XII-XII in FIG. 9B;

FIG. 13 is a cross sectional view of the EGR cooler in the fourthembodiment of the present invention similar to FIG. 11;

FIG. 14 is a perspective view of the EGR cooler in the other embodimentof the present invention;

FIG. 15 is a perspective view of the EGR cooler in the other embodimentof the present invention; and

FIG. 16 is a partial cross sectional view of an EGR cooler in the otherembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Specific embodiments of the present invention will now be describedhereinafter with reference to the accompanying drawings in which thesame or similar component parts are designated by the same or similarreference numerals.

First Embodiment

A first preferred embodiment of the present invention will be nowdescribed with reference to FIGS. 4, 5A and 5B. In the first embodiment,the present invention is typically applied to an EGR cooler of anexhaust gas recirculation system (EGR system) for a diesel engine 200(internal combustion system). FIG. 1 shows an exhaust gas heat exchanger100 (hereinafter, referred to as an EGR gas heat exchanger) that relatesto the first embodiment and a second embodiment described later.

The EGR system includes an exhaust gas recirculation pipe 210 throughwhich a part of the exhaust gas discharged from the engine 200 returnsto an intake side of the engine 200. An EGR valve 220 for adjusting theamount of exhaust gas recirculation in accordance with an operationalstate of the engine 200 is disposed in the exhaust gas recirculationpipe 210. The EGR gas heat exchanger (EGR cooler) 100 is disposedbetween an exhaust gas side of the engine 200 and the EGR valve 220 sothat heat exchange is performed between the exhaust gas discharged fromthe engine 200 and cooling water (i.e., engine-cooling water).

Next, a structure of the EGR gas heat exchanger 100 will be describedwith reference to FIGS. 5A and 5B.

EGR gas heat exchanger 100 comprises plural, in this case, four exhaustgas tubes 101 each of which has a flat rectangular cross section, andeach of which is formed by joining two plates (not shown) facing eachother. As shown in FIG. 7, an inner fin 101 b, which is for partitioningthe space formed in each exhaust gas tube 101 to form plural finepassages by being folded many times, is disposed in each exhaust gastube 101. A tank 102 has a tubular shape and a flat rectangular crosssection. This tank and the exhaust gas tubes 101 form a heat exchangingcore. The exhaust gas tubes 101 are laminated in the tank 102 so as tobe disposed in substantially parallel with each other. Moreover, alongitudinal direction of the exhaust gas tubes 101 and a longitudinaldirection of the tank 102 match with each other in the tank 102.

The tank 102 is closed at both of its side ends by core plates 103 sothat respective side ends of each exhaust gas tube 101 in the tank 102penetrate the respective core plates 103 and are supported by therespective core plates 103.

A cooling water inlet pipe 104 is connected to the tank 102 at thevicinity of root portions 101 a at upstream side portions of the exhaustgas tubes 101. Moreover, the cooling water inlet pipe 104 is connectedto the tank so as to be disposed substantially perpendicular to alaminated direction of the exhaust gas tubes 101 so that the coolingwater can easily enter each gap formed between each adjacent laminatedexhaust gas tubes 101 when the cooling water flows into the tank 102through the cooling water inlet pipe 104. A cooling water outlet pipe105 is connected to the tank 102 at the vicinity of downstream sideportions of the exhaust gas tubes 101 so that the tank 102 serves as apassage for the cooling water. The main stream of the cooling watersubstantially follows the stream of the exhaust gas passing through theexhaust gas tubes 101 in the tank 102.

Bonnets 106, 107 are connected to the both side ends of the tank 102 sothat edges of both core plates 103 are folded in opposite directionswith regard to the bonnets 106, 107 as shown the figures, and areoverlapped by end portions of the bonnets 106, 107. An exhaust gas inlet106 a is formed in the bonnet 106 disposed at a cooling water inlet pipeside that is for introducing the exhaust gas to the bonnet 106. Anexhaust gas outlet 107 a is formed in the bonnet 107 disposed at acooling water outlet pipe side that is for exhausting the exhaust gasfrom the bonnet 106 to the outside. Both of the bonnets 106, 107 have aquadrangular pyramid-like shape so that the duct cross sectional areaincreases toward the heat exchanging core.

Hereinafter, main portion of the present invention will be described. Apair of ribs 108 a, 108 b are formed as guides on both main surfaces ofeach exhaust gas pipe 101 at portions of both main surfaces close to theexhaust gas inlet 106 a by an embossing process. As shown in FIG. 5A,the ribs 108 a, 108 b have an elliptic shape so that an ellipse extendsfrom an end portion of the exhaust gas tube 101 in the width direction(longitudinal direction of the cross section) to the vicinity of acentral portion of the passage for the cooling water in the widthdirection so as to be disposed in a cross direction with respect to thelongitudinal direction of the exhaust gas tubes 101 and the longitudinaldirection of the tank 102 that matches a direction of the main stream ofthe cooling water. A small passage through which the cooling water canpass is formed between the pair of ribs 108 a, 108 b. Both ribs 108 a,108 b formed on the exhaust gas tube 101 contact to the other ribs 108a, 108 b formed on adjoining one of the exhaust gas tubes 101. Therespective pairs of ribs 108 a, 108 b formed on the respective outermain surfaces of the respective outermost exhaust gas tubes 101 omcontact to a respective protrusion 109 formed on the inner wall of thetank in the laminated direction of the exhaust gas tubes 101. Theprotrusions 109 have a shape similar to that of the pair of ribs 108 a,108 b.

In this EGR gas heat exchanger 100 described above, the exhaust gasintroduced from the exhaust gas inlet 106 a passes through the bonnet106 and each of the exhaust gas tubes 101. Then, the exhaust gas cooleddown by the cooling water flowing around each of the exhaust gas tubes101 is exhausted from the exhaust gas outlet 107 a through the bonnet107.

The cooling water flows into the tank 102 through the cooling waterinlet pipe 104 and passes through gaps formed between each adjacentexhaust gas tubes 101 and gaps formed between the inner wall of the tank102 and each of the outermost exhaust gas tubes 101 om. At the time whenthe cooling water flows into the tank 102 through the cooling waterinlet pipe 104, the cooling water coming into the tank 102 along adirection substantially perpendicular to the longitudinal direction ofthe tank 102. Therefore, the cooling water after coming into the tank102 through the cooling water inlet pipe 104 collides with an inner wall102 a of the tank 102 that is opposite to the cooling water inlet pipe104. Then, the cooling water flows so as to be divided toward therespective outermost exhaust gas tubes 101 om in the laminated directionof the exhaust gas tubes 101 (up-down direction in FIG. 5B). The dividedstreams of the cooling water go to, for example, the gaps formed betweenthe inner wall of the tank 102 and each of the outermost exhaust gastubes 101 om, and pass the gaps along the respective ribs 108 b formedon the respective outermost exhaust gas tubes 101 om to forcibly go tothe vicinity of the respective root portions 101 a (end portions ofupstream side) of the respective outermost exhaust gas tubes 101 om asshown by arrow C in FIG. 5A.

The stream C of the cooling water along the rib 108 b is merged with thestream A of the cooling water coming into the tank from the coolingwater inlet pipe 104 between the ribs 108 a and 108 b, and then, goestoward the cooling water outlet pipe 105.

According to the first embodiment, the stream C can flow along the rib108 b so as to pass the upstream side of the outermost exhaust gas tubes101 om. Therefore, the cooling water is prevented from being stuck atthe upstream side of the exhaust gas, thereby preventing the coolingwater from being boiled partially.

In this embodiment, the ribs 108 b are formed on each exhaust gas tube101. Therefore, the stream C flowing along the rib 108 b can occur atany gap formed between adjacent exhaust gas tubes 101 as well as thegaps formed between the inner wall of the tank 102 and the outermostexhaust gas tubes 101 om.

In this embodiment, the respective ribs 108 a, 108 b contact to theother respective ribs 108 a, 108 b formed on adjacent exhaust gas tube101. Also, the respective pairs of ribs 108 a, 108 b formed on therespective outer main surfaces of the respective outermost exhaust gastubes 101 om contact to the respective protrusions 109 formed on theinner wall of the tank 102. Therefore, the ribs 108 a, 108 b and theprotrusions 109 serve as reinforcement parts for reinforcing the exhaustgas tubes 101 as well as the tank and the passage for the cooling water.

In the producing process of the EGR gas heat exchanger 100, when theexhaust gas tubes 101 are connected with each other and soldered witheach other using solder, the proper load can be supplied to the exhaustgas tubes 101 and the inner fin 101 b in each exhaust gas tube 101 dueto the existence of the ribs 108 a, 108 b, whereby failure of solderingcan be prevented. Also, the ribs 108 a, 108 b keep intervals constantbetween every two of the exhaust gas tubes 101 and formed between theinner wall of the tank 102 and the outermost exhaust gas tubes 101 om.

Although the ribs 108 a, 108 b in this embodiment are formed using anembossing process, they can be formed using the other ways. For example,the ribs 108 a, 108 b can be formed discretely from the exhaust gastubes 101. Also, the shape of the ribs 108 a, 108 b is not limited tothe elliptic shape. The shape of the rib may be varied as long as itflows the cooling water after colliding the inner wall of the tanktoward the upstream side of the exhaust gas tubes 101 so as to regulatethe stream of the cooling water as shown in the FIG. 5A. Moreover, theribs can be formed only on the outermost exhaust gas tubes 101 om sincethe cooling water after colliding the inner wall 102 a of the tank 102especially easily flows toward the gaps formed between the inner wall ofthe tank 102 and the outermost exhaust gas tubes 101 om. Also, thenumber of the exhaust gas tubes 101 in the tank 102 is not limited tofour.

Second Embodiment

In the above embodiment, the ribs are used for leading the cooling waterafter colliding with the inner wall 102 a of the tank 102 toward theupstream side of the exhaust gas tubes 101.

In this embodiment, instead of the ribs, partition walls(anti-reflection boards) are used to prevent the cooling water fromflowing into the gaps formed between the inner wall of the tank 102 andthe outermost exhaust gas tubes 101 om.

As shown in FIGS. 6A, 6B, and 7, the exhaust gas tubes 101 are laminatedin 4 layers as shown in the first embodiment. Moreover, they are dividedinto two parts in each layer thereof. Inner fins 101 b and louvers 101 care formed in each exhaust gas tube 101. The louvers 101 c fixed to theinner fines 101 b are for causing vortex flow in the fine passages.

The partition walls 110 (110 a) are formed between the inner wall 102 aof the tank 102 and the exhaust gas tubes 101. The partition walls 110 aare formed by folding a plate to form the partition. That plate isdisposed between the gap formed between the inner wall 102 a of the tank102 and the exhaust gas tubes 101 so that folded portions of the platecontact to the inner wall 102 a of the tank and the exhaust gas tubes101. As shown in FIG. 7, the respective water passages 111 for thecooling water, which are formed between adjacent exhaust gas tubes 101,are partitioned from the respective water passages 112 for the coolingwater, which are formed between the inner wall of the tank 102 and theoutermost exhaust gas tubes 101 om, by the partition walls 110 a.

The cooling water flowing into the tank 102 through the cooling waterinlet pipe 104 flows into each water passage 111, 112 as shown by arrowsE in FIGS. 6A and 7. The cooling water flowing into the water passages111 is prevented from flowing into the water passages 112, and flowstoward the cooling water outlet pipe 105. Similar to the firstembodiment, the occurrence of the stuck water at the upstream side ofthe exhaust gas tubes 101, which may be caused by the interfering of thecooling water after colliding with the inner wall 102 a against thecooling water just flowing into the tank 102 through the cooling waterinlet tube 104, is prevented. Therefore, the cooling water can beprevented from being boiled partially.

Although the partition walls are formed as the anti-reflection plate byfolding the plate in this embodiment, they can be formed by the otherways. Also, the shape or size of the walls is not limited to that ofthis embodiment. Moreover, the partition walls may be used forsubstantially preventing the cooling water in the water passages 111after impacting the inner wall 102 a of the tank 102 from flowing intothe water passages 112. Therefore, a small gap can be allowed betweenthe partition walls and the exhaust gas tubes 101 or between thepartition walls and the inner wall 102 a of the tank 102 as long as thecooling water is substantially prevented from flowing into the waterpassages 112 even if the small gap exists.

In the above embodiments, the size, shape, a portion to be formed, orthe number of ribs or partition walls may be varied to effect theregulation of the stream of the cooling water.

Third Embodiment

In the above-described embodiments, the flow regulation of the coolingwater has been discussed. In embodiments described later, the flow rateof fluid for cooling the exhaust gas flowing through the exhaust gastubes, i.e., in this embodiment, the flow rate of cooling water will bediscussed to prevent the cooling water from boiling locally.

An EGR cooler (i.e., an EGR gas heat exchanger) is perspectively shownin FIG. 8. EGR gas, i.e., exhaust gas from the engine 200 as shown inFIG. 4 flows into the EGR cooler at a right side in the figure, flowsthrough the EGR cooler, and then, flows out from the EGR cooler at aleft side in the figure. Cooling water flows into the EGR cooler througha cooling water inlet pipe (a fluid inlet) 204 to exchange heat with theexhaust gas flowing through the EGR cooler. The cooling water flows outfrom the EGR cooler through a cooling water outlet pipe 205 (a fluidoutlet).

In FIG. 8, XI-XI and XII-XII mean cross sectional view points that areshown in FIGS. 11 and 12, respectively.

FIGS. 9A and 9B and numerals thereon are figures and numerals similar toFIGS. 5A and 5B, and therefore, the explanation thereof will be omitted.

In FIGS. 9A and 9B, a distribution joint 206 is for distributing theexhaust gas to the exhaust gas tubes 201. A gathering joint 207 is forgathering the exhaust gas passing through the exhaust gas tubes 201.Joint portions 206 a and 207 a of the joints 206 and 207 are connectedto exhaust gas recirculation pipe 210 shown in FIG. 4.

As shown in FIG. 10, each exhaust gas tube 201 has a flat sectionalshape through which the exhaust gas flows. The plural exhaust gas tubesare laminated in a shortest length direction, i.e., a thicknessdirection of the exhaust gas tube 201 (an up-and-down direction in FIG.10), with a space 201 a interposed between adjacent exhaust gas tubes201. The exhaust gas tubes 201 are arranged in two rows in a widthdirection of the exhaust gas tube 201 (a lateral direction in FIG. 10).In each row, four exhaust gas tubes 201 are laminated. Each exhaust gastube has two plates 201 b, 201 c that are pressed into “C”character-like sectional shape and soldered using copper solder or thelike with each other to form the shape thereof, and has a folded fin 201c to improve the heat exchange efficiency between the exhaust gas andcooling water by increasing contacting area (heat conducting area)between the exhaust gas and the fin 201 c. The folded fin is connectedto the plates 201 b and 201 c by solder using copper solder or the like.

The space 201 a is kept by contacting tops of protrusions 201 e that areprotruded from the plates 201 b and 201 c by a press process or thelike. The protrusions 201 e are discretely formed on the exhaust gastubes 201 so as not to be formed on portions in the vicinity of thecooling water inlet pipe 204 and cooling water outlet pipe 205.

For example, the exhaust gas tubes 201 and folded fins 201 d are madefrom stainless steal that is excellent in corrosion resistance and heatresistance.

The casing 202 is a rectangular pipe in which the exhaust gas tubes 201is arranged and through which the cooling water flows around the exhaustgas tubes 201. The casing 202 also is made of metal that is excellent incorrosion resistance and heat resistance, for example, stainless stealplates 202 b and 202 c fixed with each other by soldering using coppersolder or the like.

The cooling water inlet pipe 204 is provided on the casing 202 so thatthe cooling water flows into the casing 202 in a direction substantiallyperpendicular to a longitudinal direction of the exhaust gas tubes 201and substantially parallel with flat main surfaces of the exhaust gastubes 201. On the other hand, the cooling water outlet pipe 205 isprovided on the casing 202 so that the cooling water flows out from thecasing 202 in a direction substantially perpendicular to thelongitudinal direction of the exhaust gas tubes 201 and substantiallyperpendicular to the flat main surfaces of the exhaust gas tubes 201.

The cooling water inlet pipe 204 and cooling water outlet pipe 205 arefor being connected to external cooling water pipes.

As shown in FIG. 11, spaces 202 g extend between an inner wall of thecasing 202 and outermost exhaust gas tubes 201 om in a directiongenerally parallel with the inflow direction of the cooling waterflowing into the casing through the cooling water inlet pipe 204. Thewidth of the space 202 g in a laminated direction of the exhaust gastubes 201, i.e., in a direction generally perpendicular to the inflowdirection of the cooling water and perpendicular to a longitudinaldirection of the exhaust gas tubes 201 (perpendicular to a sheet of thefigure), is δ in1, as shown in FIG. 11. The width δ in1 of the spaces202 g is almost equal to the width δ t of the space 201 a betweenadjacent exhaust gas tubes 201.

Meanwhile, as shown in FIG. 12, spaces 202 h extend between the innerwall of the casing 202 and the outermost exhaust gas tubes 201 om in thevicinity of the cooling water outlet pipe 205 in a direction generallyperpendicular to an outflow direction of the cooling water flowing outfrom the casing 202 through the cooling water outlet pipe 205. The widthof the spaces 202 h in the laminated direction of the exhaust gas tubes201, i.e., in a direction generally parallel with the outflow directionof the cooling water and perpendicular to the longitudinal direction ofthe exhaust gas tubes 201 (perpendicular to a sheet of the figure), is δout, as shown in FIG. 12 (as understood from FIGS. 8, 9A and 9B). Thewidth δ out of the spaces 202 h is greater than that of the space 201 abetween adjacent exhaust gas tubes 201.

Specifically, the width δ in1 is equal to 1 mm or more but equal to 5 mmor less (2 mm in this embodiment). The width δ out is equal to 5 mm ormore (5 mm in this embodiment).

The lower limit of the width δin1 is defiled in such a degree that thespaces 202 g that serve as cooling water passages are prevented frombeing clogged with extraneous substance in the cooling water. Meanwhile,the upper limit of the width δ in1 is defiled in such a degree that theflow rate of the cooling water flowing through the spaces 202 g is notlowered lower than a predetermined rate.

Most of the cooling water flowing into the casing 202 through thecooling water inlet pipe 204 flows through the spaces 201 a betweenspaces 201 a facing the cooling water inlet pipe 204, i.e., spaces 201 aformed between two exhaust gas tubes 201 in the second and third layers.Then, most of the cooling water collides with the inner wall of thecasing 200 that is opposite to the cooling water inlet pipe 204 (a rightside wall in FIG. 11).

Therefore, the mass flow of the cooling water is smaller in the spaces202 g than in the spaces 202 a because the spaces 202 g are farther awayfrom the space 201 a between the exhaust gas tubes 201 in the second andthird layers in the direction perpendicular to the inflow direction ofthe cooling water and perpendicular to the longitudinal direction of theexhaust gas tubes 201 (perpendicular to a sheet of the figure).Accordingly, the flow rate in the spaces 202 g become small. As aresult, the cooling water might be likely boiled at the spaces 202 g.

In this embodiment, the spaces 202 g are regulated in width of δ in1similar to that of δ in1 of the spaces 201 a to prevent the flow ratetherein from being lowered lower than the predetermined rate. Therefore,the local boiling of the cooling water is prevented at the spaces 202 g.

Similar to the spaces 202 g, the width δ t of the spaces 201 a isselected between the width with which the spaces 201 a are preventedfrom being clogged with extraneous substance in the cooling water andthe width with which the flow rate of the cooling water flowing throughthe spaces 201 a is not lowered lower than the predetermined rate.

To the contrary, the cooling water is collected in the vicinity of thecooling water outlet pipe 205 after flowing through the casing 202.Therefore, if the width δ out of the spaces 202 h was small, thepressure loss might be increased at the spaces 202 h that might reducethe amount of the cooling water flowing into the EGR cooler 200. In thissituation, the local boiling might be caused.

In this embodiment, the width δ out of the spaces 202 h in the vicinityof the cooling water outlet pipe 205 is greater than the width δ t ofthe spaces 201 a between adjoining exhaust gas tubes 201 to prevent thepressure loss from being increased. Therefore, the cooling water flowinginto the casing 202 is prevented from decreasing, thereby preventing thelocal boiling of the cooling water from occurring and preventing coolingefficiency of the exhaust gas from being lowered.

Moreover, as shown in FIG. 11, spaces 202 j are formed between innerwalls of the casing 202 that are disposed generally perpendicular to theinflow direction of the cooling water and sides of the exhaust gas tubes201. The width of the spaces 202 j in a direction generally parallelwith the inflow direction of the cooling water, i.e., in a paralleldirection of the figure, is δ in2. The width δ in2 is substantiallyequal to the width δ t of the spaces 201 a between adjoining exhaust gastubes 201 for the same reason described above.

Fourth Embodiment

In this embodiment, differences between the third embodiment and thisembodiment will be mainly described.

As shown in FIG. 13, the width δ in2 of the spaces 202 j is greater thanthe width δ t of the spaces 201 a. Specifically, the width δ in2 of thespaces 202 j is equal to 5 mm or more (5 mm in this embodiment), thewidth δ in1 of the spaces 202 g is equal to 1 mm or more but equal to 5mm or less (2 mm in this embodiment), and the width δ out of the spaces202 h is equal to 5 mm or more (5 mm in this embodiment).

With this feature, the distribution efficiency of the cooling water toeach space 201 a between each adjacent exhaust gas tube 201 in thelaminated direction can be improved. Moreover, the pressure loss in thevicinity of the cooling water outlet pipe 205 can be reduced.

Although the spaces 202 h are greater in width than the spaces 202 g inthe above-described embodiments, it is not necessarily to form the widerspaces 202 h. Instead of changing the shape of the casing 202, the sizeor the location of the exhaust gas tubes 201 can be varied to match thesize dimension of the width of spaces 202 g with that of the spaces 201a.

The space between the exhaust gas tubes 201 and the inner wall of thecasing 202 is formed wider in the vicinity of the cooling water outletpipe 205 at entirely circumference as shown in FIG. 8. However, as shownin FIG. 14, the wider portion of the casing 202 may be limited to aportion where the spaces 202 h are located between the inner wall of thecasing 202 and the outermost exhaust gas tubes 201 om in the vicinity ofthe cooling water outlet pipe 205 in the laminated direction of theexhaust gas tubes 201 and a portion close to the outlet side withrespect to the inlet side of the casing where the spaces 202 h arelocated between the inner wall of the casing 202 and the outermostexhaust gas tubes 201 om at an opposite side of the portion where thecooling water outlet pipe 205 is located in the laminated direction.

Moreover, the spaces 202 h in the outlet side of the casing 202 may beformed so that the width thereof is identical to that of the spaces 201a between adjacent exhaust gas tubes 201 similar to the spaces 202 g inthe inlet side of the casing 202.

Moreover, as shown in FIG. 16, ribs 208 a or ribs 208 b also can beformed on each exhaust gas tube 201 that are shown FIGS. 5A and 5B so asto regulate the flow of the cooling water in addition to keeping theflow rate of the cooling water in the casing 202 by adjusting the sizeof the spaces.

While the present invention has been shown and described with referenceto the foregoing preferred embodiment, it will be apparent to thoseskilled in the art that changes in form and detail may be thereinwithout departing from the scope of the invention as defined in theappended claims.

1. An exhaust gas heat exchanger comprising: a plurality of exhaust gastubes through which exhaust gas generated by combustion flows; a casingin which the plurality of exhaust gas tubes are arranged, defining afluid passage therein through which fluid flows around the plurality ofexhaust gas tubes to exchange heat with the exhaust gas; a fluid inletdisposed on the casing at an inlet side of the plurality of exhaust gastubes through which the fluid flows into the casing along a directionsubstantially perpendicular to a longitudinal direction of the pluralityof exhaust gas tubes; and an outer space defined between an inner wallof the casing and an outermost exhaust gas tube of the plurality ofexhaust gas tubes, and extending longitudinally in a directionsubstantially parallel with an inflow direction of the fluid flowinginto the casing through the fluid inlet, wherein: a width of the outerspace, in a direction substantially perpendicular to the inflowdirection of the fluid and substantially perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes, issubstantially equal to that of an inner space defined between adjacentexhaust gas tubes.
 2. An exhaust gas heat exchanger comprising: aplurality of exhaust gas tubes through which exhaust gas generated bycombustion flows; a casing in which the plurality of exhaust gas tubesare arranged, defining a fluid passage therein through which fluid flowsaround the plurality of exhaust gas tubes to exchange heat with theexhaust gas; a fluid inlet disposed on the casing at an inlet side ofthe plurality of exhaust gas tubes, through which the fluid flows intothe casing along a direction substantially perpendicular to alongitudinal direction of the plurality of exhaust gas tubes; and anouter space defined between an inner wall of the casing and an outermostexhaust gas tube of the plurality of exhaust gas tubes, and extendinglongitudinally in a direction substantially parallel with an inflowdirection of the fluid flowing into the casing through the fluid inlet,wherein: a width of the outer space, in a direction substantiallyperpendicular to the inflow direction of the fluid and substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes, is equal to or greater than 1 mm but equal to or less than 5mm.
 3. An exhaust gas heat exchanger according to claim 1, wherein eachexhaust gas tube has a flat sectional shape, and the plurality ofexhaust gas tubes are laminated in a thickness direction thereof withthe inner space defined between adjacent exhaust gas tubes, and whereinthe inflow direction of the fluid is substantially perpendicular to alaminated direction of the plurality of exhaust gas tubes.
 4. An exhaustgas heat exchanger according to claim 1, further comprising: a fluidoutlet disposed on the casing through which the fluid flows out from thecasing in a direction substantially perpendicular to the longitudinaldirection of the plurality of exhaust gas tubes; and an outlet sideouter space defined between the inner wall of the casing and theoutermost exhaust gas tube at the vicinity of the fluid outlet,extending longitudinally in a direction substantially perpendicular toan outflow direction of the fluid flowing out from the casing, wherein:a width of the outlet side outer space, in a direction substantiallyparallel with the outflow direction of the fluid, is greater than thatof the inner space defined between adjacent exhaust gas tubes.
 5. Anexhaust gas heat exchanger according to claim 1, further comprising: afluid outlet disposed on the casing, through which the fluid flows outfrom the casing in a direction substantially perpendicular to thelongitudinal direction of the plurality of exhaust gas tubes; and anoutlet side outer space defined between the inner wall of the casing andthe outermost exhaust gas tube at the vicinity of the fluid outlet,extending longitudinally in a direction substantially perpendicular toan outflow direction of the fluid flowing out from the casing throughwhich the fluid outlet, wherein: a width of the outlet side outer space,in a direction substantially parallel with the outflow direction of thefluid, is equal to or greater than 5 mm.
 6. An exhaust gas heatexchanger according to claim 1, further comprising: a side space definedbetween a side inner wall of the casing and the plurality of exhaust gastubes, extending longitudinally in a direction substantiallyperpendicular to the inflow direction of the fluid, wherein a width ofthe side space, in a direction substantially parallel with the inflowdirection of the fluid, is equal to or greater than that of the innerspace defined between adjacent exhaust gas tubes.
 7. An exhaust gas heatexchanger according to claim 1, further comprising: a side space definedbetween a side inner wall of the casing and the plurality of exhaust gastubes, extending longitudinally in a direction substantiallyperpendicular to the inflow direction of the fluid, wherein a width ofthe side space, in a direction substantially parallel with the inflowdirection of the fluid, is equal to or greater than 1 mm.
 8. An exhaustgas heat exchanger according to claim 1, further comprising: a fluidflow regulating means provided in the fluid passage close to an upstreamside of the plurality of exhaust gas tubes for regulating a stream ofthe fluid at a vicinity of the upstream side of the plurality of exhaustgas tubes so that the fluid after colliding with a side inner wall ofthe casing is led toward an upstream side of the plurality of exhaustgas tubes.
 9. An exhaust gas heat exchanger according to claim 2,wherein each exhaust gas tube has a flat sectional shape, and theplurality of exhaust gas tubes are laminated in a thickness directionthereof with an inner space defined between adjacent exhaust gas tubes,and wherein the inflow direction of the fluid is substantiallyperpendicular to a laminated direction of the plurality of exhaust gastubes.
 10. An exhaust gas heat exchanger according to claim 2, furthercomprising: a fluid outlet disposed on the casing through which thefluid flows out from the casing in a direction substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes; and an outlet side outer space defined between the inner wallof the casing and the outermost exhaust gas tube at the vicinity of thefluid outlet, extending longitudinally in a direction substantiallyperpendicular to an outflow direction of the fluid flowing out from thecasing, wherein: a width of the outlet side outer space, in a directionsubstantially parallel with the outflow direction of the fluid, isgreater than that of the inner space defined between adjacent exhaustgas tubes.
 11. An exhaust gas heat exchanger according to claim 2,further comprising: a fluid outlet disposed on the casing, through whichthe fluid flows out from the casing in a direction substantiallyperpendicular to the longitudinal direction of the plurality of exhaustgas tubes; and an outlet side outer space defined between the inner wallof the casing and the outermost exhaust gas tube at the vicinity of thefluid outlet, extending longitudinally in a direction substantiallyperpendicular to an outflow direction of the fluid flowing out from thecasing through which the fluid outlet, wherein: a width of the outletside outer space, in a direction substantially parallel with the outflowdirection of the fluid, is equal to or greater than 5 mm.
 12. An exhaustgas heat exchanger according to claim 2, further comprising: a sidespace defined between a side inner wall of the casing and the pluralityof exhaust gas tubes, extending longitudinally in a directionsubstantially perpendicular to the inflow direction of the fluid,wherein a width of the side space, in a direction substantially parallelwith the inflow direction of the fluid, is equal to or greater than thatof the inner space defined between adjacent exhaust gas tubes.
 13. Anexhaust gas heat exchanger according to claim 2, further comprising: aside space defined between a side inner wall of the casing and theplurality of exhaust gas tubes, extending longitudinally in a directionsubstantially perpendicular to the inflow direction of the fluid,wherein a width of the side space, in a direction substantially parallelwith the inflow direction of the fluid, is equal to or greater than 1mm.
 14. An exhaust gas heat exchanger according to claim 2, furthercomprising: a fluid flow regulating means provided in the fluid passageclose to an upstream side of the plurality of exhaust gas tubes forregulating a stream of the fluid at a vicinity of the upstream side ofthe plurality of exhaust gas tubes so that the fluid after collidingwith a side inner wall of the casing is led toward an upstream side ofthe plurality of exhaust gas tubes.